Nestable interlocking seal blank



April 1963 w. F. KUSTER 3,083,845

NESTABLE INTERLOCKING SEAL. BLANK Filed Sept. 15, 1961 2 Sheets-Sheet l IN V EN TOR:

April 2, 1963 w. F. KUSTER NESTABLE INTERLOCKING SEAL BLANK 2 Sheets-Sheet 2 Filed Sept. 15, 1961 2/, QZINVENTORJ BY WM fi United States Patent Filed Sept. 15, 1961, Ser. No. 138,45)? 8 Claims. or. 214-105) T he present invention relates to an improved nestable seal blank, useful in forming a seal or a joint between the overlapping portions of bundle encircling metallic strapping, or in forming a connection between overlapping or juxtaposed portions of wire, strapping and the like, and in particular it relates to a new and improved arrangement for itiemporarily securing nested seal blanks in a stick or stac Nesting type seal blanks as generally shown in George A. Crosby Patent No. 2,344,804, dated March 31, 1944, or John H. Leslie ll Patent No. 2,610,374, dated September 16, 1952, comprise a substantially flat back plate having a width equal to the width of the strapping with which the blank is to be used and a pair of flaring or diagonally outwardly extending flanges, so that a stack of such seal blanks may be formed by nesting one within the next adjacent blank. The seal blanks are usually separated from each other by sliding one longitudinally outwardly from one end of the stack-usually the inner seal is slid from the stack into the joint forming mechanism of the strapping machine or tool. Such seals, arranged in stacks, may be used in power strapping machines of the types shown in Paul A. Chamberlain Patent No. 2,43 8,386, dated March 23, 1948, John H. Leslie and George A. Crosby Patent Nos. 2,707,429 and 2,707,430, dated May 3, 1955, George A. Crosby and Robert J. Frey Patent No. 2,801,558, dated August 6, 1957, and George A. Crosby and Howard K. Otto Patent No. 2,915,003, dated Decemher 1, 1959, and in hand operated tools of the types shown in John H. Leslie II Patent No. 2,497,313, dated February 14, 1950, and William C. Childress and Arvid -I. Ericsson Patent No. 2,594,397, dated April 29, 1952. These machines and tools all possess a seal blank storage magazine which is adapted to receive a stack of nested seal blanks, and they all have some seal blank feeding mechanism synchronized with the operation of a joint forming mechanism for stripping a single blank from the end of the stack in the magazine and delivering it into the jaws of the joint forming mechanism.

Previously, the nested seal blanks were retained in the stack by passing a loop of wire through aligned holes punched in the centers of the back plates in the manner shown in Patent No. 2,344,804. As the seal blanks were loaded into the magazine of the machine or tool the wire loop was removed and the blanks could be separated from the stack one at a time by the feeding mechanism. Such blanks had certain objectionable features. The holes formed in the back plate met with some objections from users who have their trademarks or names lithographed on the seal blank as the hole frequently marred the design or removed a letter from the name. There was always the added expense of threading the wire through the holes plus the cost of the wire itself. It has also been found that the part of the blank forming die which made the hole was the first to wear out.

There have been developments in the past several years which sought to overcome the above mentioned disadvantages, but the seal blanks of these developments also had certain disadvantages or raised certain problems. In one of these developments the flanges were both formed with longitudinal grooves extending the full flange length and the very outer edges of the flanges were bent inwardly to engage in the grooves of the blank with which the first 3,083,845 Patented Apr. 2, 1963 blank was nested. Such blanks when nested and interlocked formed a rigid stick or stack and unless the blanks were very precisely made the stack would be curved in one direction or another and would not fit into the machine or tool magazine without jamming. Obviously the dies for making such blanks would be complex and expensive and have portions that would wear out rapidly and need replacement. Another disadvantage of such lanks is the impossibility of making a small and compact joint since the flanges provide humps on either side of the longitudinal groove which are not flattened by the jaws of the joint forming mechanisms usually embodied in commercially available strapping machines and tools. Furthermore, the presence of the full length grooves in the flanges with the bounding bumps and inturned flange edges increase the possibility of this blank jamming in the jaws of mechanisms which were not specifically designed to use this seal blank.

Another and more recent attempt to overcome the disadvantages of the prior blanks including that just described produced a blank with flat surfaced flange faces except for a small are or crescent shaped groove on the outer flange face and an inwardly pointing projection on the inner flange face which engaged in the groove on the outer flange face of a second blank nested within the first blank. These blanks overcame most of the disadvantages found in the earlier seal blanks and met with substantial commercial success. They did, however, present problems in manufacture which gave rise to troubles in the field. For example, variations in the thickness of the metal stock from which the blanks were made caused variations in the groove depth which would frequently adversely affect the fitting qualities in the stack. In order .to insure articulation of the stack in four dimensions it is necessary to provide sufilcient clearance between blanks. :In order to obtain this clearance with this blank it proved to be necessary to make the arcuate grooves excessively deep to prevent shoaling to the point where the seal blanks would not properly snap-in and hold. Also it was found that tool and die costs and manufacturing expenses were higher than thought compatible with good business practices. It also developed that the push away action of the blanks during separation of a blank from the stack and provided by the arcuate groove sometimes would cock the blank during the delivery action and either jam it in the delivery path or in the jaws of the joint forming mechanism.

The sealblank of the present invention greatly modifies the groove and nib conformations of the prior art and under tests has demonstrated that the disadvantages, dil'liculties and problems which have been encountered in the past have been overcome.

It is, therefore, the principal object of the present invention to provide a new and improved nestable and interlocking seal blank which overcomes the disadvantages of the prior blanks.

Another object is to provide a new and improved seal blank wherein variations of the stock thickness have little or no effect upon the fitting, nesting and interlocking qualities of the seal blanks in the stack.

Another object is to provide a new and improved seal blank wherein the interlocking groove and nib can be made with sutficient clearance so as to permit articulation in all four directions-two longitudinally of the blanks and two transversely of the blanksthus making it easier to assemble a straight stack and removing any likelihood of the stack' jamming in the machine or tool magazine.

Another object is to provide a new and improved nestable and interlocking seal blank which may be stripped from the delivery end of a stack and carried to the joint forming mechanism of a strapping machine or tool with 'a a little possibility that the blank will cock and jam the machine or tool.

Another object is to provide a new and improved nestable and interlocking seal blank which is easier and less expensive to make than the earlier blanks and can be made with greater tolerances and less expensive dies.

Another object is to provide new and improved nestable and interlocking seal blanks assembled into a stack which does not bridge or arch in the seal magazine.

Another object is to provide a new and improved nestable and interlocking seal blank having a short rectangular groove in the outer face of each flange and a rectangular nib'on the inner face of each flange with the groove and nib being formed with sloping end walls to facilitate endwise disengagement of interlocked blanks.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawings wherein:

FIG. '1 is a perspective view of a seal blank made in accordance with the present invention;

FIG. 2 is a transverse sectional view through a group of nested and interlocked seal blanks, showing the manner in which the seal blanks are clipped one to another to form a stack or stick of seal blanks;

FIG. 3 is a greatly enlarged elevational view of a portion of the outer face of the flange of a seal blank 1 showing the details of the interlock groove and the dimple made during the formation of the interlock projection or nib;

FIG. 4 is an elevational view on the same scale as FIG. 3 of a portion of the inner face of the flange showing the interlock projection or nib;

FIG. 5 is a sectional view taken along the line 5--5 of FIG. 3, looking in the direction of the arrows;

FIG. 6 is a sectional View taken along the line 6-6 of FIG. 3, looking in the direction of the arrows;

FIG. 7 is a perspective view, similar to FIG. 1, of a second form of seal blank made in accordance with the present invention;

FIG. 8 is an elevational view of a stack or stick of seal blanks assembled from a plurality of the blanks shown in FIG. 8 and indicating by broken lines the total amount of endwise play in the stack;

FIG. 9 is an elevational view of the opposite side of the stack shown in FIG. 8 and indicating by broken lines the amount of articulation permitted longitudinally of the seal blanks; and

FIG. 10 is an elevational view of the right side of the stack as shown in FIG. 9 and indicating by broken lines the amount of articulation permitted transversely of the seal blanks.

In the drawings the reference character indicates the seal blank as formed of a single metallic piece with a back portion or plate 22, the width of which is equal to or only slightly greater than the width of the strapping with which the seal blank is to be used. The back plate is bounded along its-parallel edges 24 by a pair of flanges 26 integral therewith and which when the blank is initially formed project diagonally outwardly from the back plate 22. The flaring flanges permit the stacking and nesting of the seal blanks, as shown in FIGS. 2 and 8 to 10, for convenience in shipping and handling and for insertion into the storagemagazine of a strapping tool or strapping machine of any of the types mentioned herein-- above. When the tension resisting joint is formed between the overlapping portions of the strapping, the flanges 26 are folded about the strapping and the blank 20 and strapping portions are deformed in a manner well known in this art to lock the strapping portions and the seal blank into a tension resisting joint.

As explained above, it has been customary in the past to provide centrally located apertures in the back plate 22 and to pass a retaining wire through the apertures to hold the nested blanks in the stack and prevent them from becoming accidentally separated from each other during shipment and handling. According to the present invention, the flanges 26 are provided with means 28 for interlocking the nested seal blank-s one to the next so that they will be held in a stack in the manner shown in detail in FIG. 2. This clipping or interlocking means 28 includes a projection or nib 30 formed on and upstanding from the inner face 32 of each of the flanges at the longitudinal center thereof. The nib 30' is positioned to engage in a groove 34 also longitudinally extending and formed in the outer face 35 of each of the flanges at the longitudinal center thereof but positioned closer to the back plate 22 than the projection or nib so as to be engaged by the latter in the manner shown in FIG. 2.

In manufacturing the seal blank 20 the nib or projection 30 and groove 34 are formed simultaneously.

The nib 30 is formed against an anvil which has a slot therein and into which the metal is deformed by a male die which punches a conically shaped depression 38 into the flange 26 from the outer face 36 thereof. This causes the metal to flow into the slot in the anvil thereby forming the nib 30. It will be observed that the included angle defined by the conical depression 38 is 60 and that the side walls 40 of the nibdefine an angle of 60 with a plane normal to the inner face 32 of the flange 26 or an obtuse angle of with the inner face 32. The ends of the nib 30 are sloped at 42 to define an angle of about with the inner face 32.

The groove 34 formed in the outer face 36 of the flangeis formed by a male die against a flat anvil so that as seen in cross section (FIG. 5) there is no upsetting of metal on the inner face 32 of the flange. The groove 34 has its long dimension parallel to the outer edge of the flange and the marginal edge 24 of the back plate. The configuration of the groove 34 is best seen in FIGS. 3, 5 and 6 and it has a pair of sloping end faces 44 and a sloping side 46 which intersect the outer face 36 of the flange 26 at an angle of approximately 30. The fourth wall' 48 of the groove 34 intersects the surface 36 at an angle of about 45. The end walls or sloping surfaces 44 cooperate with the sloping ends 42 on the nib or projection 30 so that when one of the seal blanks is slid relative to the other, a surface 42 slides up a surface 44, the two being substantially parallel, so that a minimum amount of force may be used endwise to slide one of the seal blanks relative to its adjacent nested blank.

On the other hand, :the surface 48 slopes at a much sharper angle toward the surface 36 so as to cooperate with the inner surface 40 of the projection 30 to provide the interlock against vertical separation of the seal blanks, that is, vertical with respect to FIG. 2. However, these surfaces do not lie contiguously face-to-face due to different angles involved, and a small amount of play is permitted giving a clearance of approximately .001 to .002 inch thereby facilitating articulation of the nested seal blanks in all fourdirections, that is, the two direc tions longitudinally of the blanks and the two directions transversely of the blanks.

It will be observed that the nib 30 has a broad and somewhat flattened crown surface 50 and that the groove 34 has a flat bottom 52. The proportions are such, however, that the crown of the nib does not contact the bottom 52 of the groove thereby insuring the clearance and play mentioned above.

It should be noted that the groove 34 is made with a die which has flat surfaces upon it which define the bottom 52, end walls 44 and side walls 46 and 48 and that the groove and the anvil which is used to form the nib 30 similarly has flat surfaces which define the side Walls 40. The only curved surface in the die system is the conical pin which is used in forming the dimple 38. It is readily apparent, therefore, that the dies of this systern, due to their configuration of having primarily flat or simple geometrical surfaces, are relatively inexpensive to form with substantial accuracy, and they of course may be renovated with no difliculty. This is in sharp contrast with one of the prior art developments mentioned above wherein the groove was arcuate or crescent shaped and the nib or projection was circular or conical. In that development it was necessary to maintain extreme accuracy in the dies which resulted in rather substantial expenditures.

The seal blanks 20 of this invention may be clipped together by forcing them vertically downwardly, one on top of the other, in a direction parallel to the surface of the drawing as seen in FIG. 2 thereby engaging the nibs 3% into the grooves 34, the locking coming between the uppermost of the walls 40 and the sloped wall 48 of the groove. When it is desired to strip the innermost of the nested seal blanks from the remainder of the stack or stick, it is slid longitudinally in a straight line and an end wall 42 of the nib will ride easily up the end wall 44 of the groove of the seal blank being moved. Since there is a certain amount of flexibility in the flanges of the seal blank, this operation can be carried out with the application of a positive and yet not overly strong force. The seal blanks will move in a straight line in separating, and consequently there will be no tendency of the blank to cock as it is being delivered from the magazine to the jaws of the joint forming mechanism.

In FIGS. 1 to 6 there has been shown and illustrated a seal blank adapted for use with one and one quarter inch strapping. However, the same proportions will be found in seal blanks used with strapping of larger as well as substantially smaller widths, and blanks intended for use with wire and the like will be similarly formed. It is not intended by this invention to relate the arrangement to specific dimensions but only to the relative positions of the nibs and grooves and the angularity of the surfaces which provide the interlock as well as the surfaces 44 and 42 which facilitate the removal of one blank from the next.

In FIGURES 7 through there are shown slightly modified blanks 54 connected and clipped together into a stick or stack 56. The blank 54 is substantially the same as the blank 2! and has a back plate 58 to which are connected a pair of diagonally outwardly extending flanges 60 along the parallel edges of the back plate 58. The blank 54 is provided with a pair of interlocking means 62, 64 on one of the flanges 60 and a single interlocking means 66 on the other flange. Each of the interlocking means comprises a groove 68 which in all respects is identical with or substantially similar to the groove 34 on the outer face of the flange and an inwardly projecting nib or tooth 70 identical with or substantially similar to the nib 30 on the inner face of the flange and consequently these specific elements will not be separately described.

When the seal blanks 54 are assembled into the stack 56, the interlocking means 62 of one blank will be engaged with the interlocking means 62 of the juxtaposed and nested blank, and likewise the interlocking means 64 and 66 will be engaged with their counterparts throughout the entire stack.

It has been shown in FIGURES 8, 9 and 10 the looseness or clearance in the stack which is cumulative from the bottom blank 54 through the entire group of nested and interlocked seal blanks 54. The stacks or sticks 56 shown in FIGURES 8, 9 and 10 include approximately fifty-five seal blanks adapted for use with five-eighths inch strapping and are drawn substantially to scale. It will be observed in FIGURE 8 by the broken line 72 the amount of vertical expansion that the entire stack has which is the cumulative effect of all of the clearances and play in the interlocking means 62, 64 and 66 which permit the articulation shown in FIGS. 9 and 10. In FIG. 9 the broken lines 74 indicate the amount of articulation longitudinally of the seal blank, that is, in the direction of strap extension through the blank as it is applied to the strapping. It will be seen that is quite extreme, and it is accomplished by virtue of the use of two interlocking means 62, 64 on one flange and a single interlocking means 66 at the other flange. In FIGURE 10 the broken line 76 indicates the amount of articulation or bending of the stack toward the flanges having the double interlocking means 62 and 64- while the similar line 78 indicates the transverse bending toward the side of the stack wherein the flanges are interconnected by a single interlocking means '66. This figure shows that the double interlocking means 62, 64 on one side permits less articulation or bending than does the single one as might be expected.

However, the entire arrangement provides that when the seal blank stick 56 is inserted into the magazine of a strapping machine, such for example that shown in the previously mentioned Patent No. 2,707,430 where the magazine is disposed in a horizontal plane and a force is used to urge the stick or stack toward the outlet or delivery end of the magazine, there will be little or no tendency for the stack 56 to hump, that is, bend upwardly or break upwardly in the magazine because the articulation is gradual and controlled over the entire length of the stick or stack due to the distribution of the forces tending to hump the stack through the single interlocking means on one side and the double interlocking means on the other side. In this connection it should be noted that the seal blanks are positioned in the magazine along their open edges so that looking down into the magazine from above, the blanks will be seen as shown in FIG. 10.

It will be seen, therefore, from the foregoing description that a new and improved nestable and interlocking seal blank has been provided which attains all of the objectives claimed for the present invention in the opening paragraphs.

While two embodiments of the seal blank constituting this invention have been shown and described, it will be apparent that modifications and variations thereof may be made without departing from the underlying principles of the invention. It is therefore desired by the following claims to include within the scope of the invention all such variations and modifications by which substantially the results of this invention may be obtained through the use of substantially the same or equivalent means.

What is claimed as new and desired to be secured by United States Letters Patent is:

1. In a seal blank useful in forming a connection between overlapping portions of metallic strapping, wire and the like and adapted to be nested and interlocked with another and similarly formed seal blank, having a back plate to which is joined a pair of diagonally outwardly extending rectangular flanges along the side edges thereof, each flange having generally plain inner and outer faces, the improvement which comprises a small elongate projection upstanding from the inner face of each flange with the long dimension of said projection parallel to the outer edge of the flange, said projection having gradually sloping ends and inwardly tapering sides, and an elongate rectangular slot in the outer surface of each flange positioned directly closer to the back plate than said projection and with its long dimension parallel to the outer edge of the flange, said slot having gradually inwardly and downwardly sloping end walls, and said slot having a sharply inwardly and downwardly sloping side wall remote from the outer edge of the flange and adapted to be engaged by the tapering side of a projection of a similarly formed seal blank to secure the blanks together in nested relationship with slight movement of the nested blanks in four directions, said blanks being disengaged by sliding one blank relative to the other so that one sloping end of the projection will slide on a sloping end wall of the slot in which the projection is engaged.

2. A seal blank as claimed in claim 1, wherein one flange is formed with a longitudinally centered projection and slot and the other flange is formed with a pair of symmetrically positioned projections and slots.

spar-Jean 3.111 a seal blank useful in forming a connection between overlapping portions of metallic strapping, wire and the like and adapted to be nested and interlocked with another and'similarly formed seal blank, having a back plate to which is joined a pair of diagonally outwardly extending rectangular flanges along the side edges thereof, each flange having generally plain inner and outer faces, the improvement which comprises a small elongate projection upstanding from the inner face of each flange with the long dimension of said projection parallel to the outer edge of the flange, said projection having sloping ends and inwardly tapering sides, and an elongate rectangular slot in the outer surface of each flange positioned directly closer to the back plate than said projection and with its long dimension parallel to the outer edge of the flange, said slot having gradually inwardly and downwardly sloping end walls and that side wall closest to the outer edge of the flange, and said slot having a sharply inwardly and downwardly sloping side wall opposite said first side wall adapted to be engaged by the tapering side of aprojection of a similarly formed seal blank to secure the blanks together in nested relationship with slight movement of the nested blanks in four directions, said blanks being disengaged by sliding one blank relative to the other so that one sloping end of the projection will slide on a sloping end wall of the slot in which the projection is engaged.

4. In a seal blank useful in forming a connection between overlapping portions of metallic strapping, wire and the like :and adapted to be nested and interlocked with another and similarly formed seal blank, having a back plate to which is joined a pair of diagonally outwardly extending rectangular flanges along the side edges thereof, each flange having generally plain inner and outer faces, the improvement which comprises a small elongate projection upstanding from the inner face of each flange with the long dimension of said projection parallel to the outer edge of the flange, said projection having sloping ends, each making an angle of about 150 with the flange inner face, and inwardly tapering sides, and an elongate rectangular slot in the outer surface of each flange positioned directly closer to the back plate than said projection and with its long dimension parallel to the outer edge of the flange, said slot having inwardly and downwardly sloping end walls making an angle of about 30 with the flange outer face, and said slot having a sharply inwardly and downwardly sloping side wall remote from the outer edge of the flange and adapted to be engaged by the tapering side of a projection of a similarly formed seal blank to secure the blanks together in nested relationship with slight movement of the nested blanks in four directions, said blanks being disengaged by sliding one blank relative to the other so that one sloping end of the projection will slide on a sloping end wall of the slot in which the projection is engaged.

5. In a seal blank useful in forming a connection between overlapping portions of metallic strapping, wire and the like and adapted to be nested and interlocked with another and similarly formed seal blank, having a back plate to which is joined a pair of diagonally outwardly extending rectangular flanges along the side edges thereof, each flange having generally plain inner and outer faces, the improvement which comprises a small elongate projection upstanding from the inner face of each flange with the long dimension'of said projection parallel to the outer edge of the flange, said projtction having sloping ends, each making an angle of about 150 with the flange inner face, and inwardly tapering sides, each making an angle of about with the flange inner face, and an elongate rectangular slot in the outer surface of each flange positioned directly closer to the back plate than said projection and with its long dimension parallel to the outer edge of the flange, said slot having gradually inwardly and downwardly sloping end walls and that side wall closest to the outer edge of the flange, each of said walls making an angle of about 30 with the flange outer face, and said slot having a sharply inwardly and downwardly sloping side wall opposite said first side wall making an angle of about 45 with the flange outer face and adapted to be engaged by the tapering side of a projection of a similarly formed seal blank to secure the blanks together in nested relationship with slight movement of the nested blanks in four directions, said blanks being disengaged by sliding one blank relative to the other so that one sloping end of the projection will slide on a sloping end wall of the slot in which the projection is engaged.

6. A seal blank as claimed in claim 5, wherein one flange is formed with a longitudinally centered projection and slot and the other flange is formed with a pair of symmetrically positioned projections and slots.

7. A stack of seal blanks useful in forming connections between overlapping portions of metallic strapping, wire and the like, the blanks being nested and interlocked with one another and each having a back plate to which is joined a pair of'diagonally outwardly extending rectangm lar flanges along the side edges thereof, each flange having I generally plain inner and outer faces, each flange having at least one small elongate projection upstanding from the inner face of the flange with the long dimension of said projection parallel to the outer edge of the flange, said projection having gradually sloping ends and inwardly tapering sides, and at least one elongate rectangular slot in the outer surface of the flange positioned directly closer to the back plate than said projection and with its long dimension parallel to the outer edge of the flange, said slot having gradually inwardly and downwardly sloping end walls and that side wall closest to the outer edge of the flange, and said slot having a sharply inwardly and downwardly sloping side wall opposite said first side wall adapted to be engaged by the tapering side of a projection of the adjacent seal blank thereby to secure theblanks together in nested relationship in the stack with slight movement of the nested blanks in four directions, said blanks being disengaged from the stack by sliding the end blank relative to the stack so that one sloping end of the projection will slide on a sloping end wall of the slot in which the projection is engaged.

8. A stack of seal blanks as claimed in claim 7, wherein one of the flanges is formed with a single longitudinally centered projection and slot and the other flange is formed with a pair of symmetrically positioned projections and slots.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A SEAL BLANK USEFUL IN FORMING A CONNECTION BETWEEN OVERLAPPING PORTIONS OF METALLIC STRAPPING, WIRE AND THE LIKE AND ADAPTED TO BE NESTED AND INTERLOCKED WITH ANOTHER AND SIMILARLY FORMED SEAL BLANK, HAVING A BACK PLATE TO WHICH IS JOINED A PAIR OF DIAGONALLY OUTWARDLY EXTENDING RECTANGULAR FLANGES ALONG THE SIDE EDGES THEREOF, EACH FLANGE HAVING GENERALLY PLAIN INNER AND OUTER FACES, THE IMPROVEMENT WHICH COMPRISES A SMALL ELONGATE PROJECTION UPSTANDING FROM THE INNER FACE OF EACH FLANGE WITH THE LONG DIMENSION OF SAID PROJECTION PARALLEL TO THE OUTER EDGE OF THE FLANGE, SAID PROJECTION HAVING GRADUALLY SLOPING ENDS AND INWARDLY TAPERING SIDES, AND AN ELONGATE RECTANGULAR SLOT IN THE OUTER SURFACE OF EACH FLANGE POSITIONED DIRECTLY CLOSER TO THE BACK PLATE THAN SAID PROJECTION AND WITH ITS LONG DIMENSION PARALLEL TO THE OUTER EDGE OF THE FLANGE, SAID SLOT HAVING GRADUALLY INWARDLY AND DOWNWARDLY SLOPING END WALLS, AND SAID SLOT HAVING A SHARPLY INWARDLY AND DOWNWARDLY SLOPING SIDE WALL REMOTE FROM THE OUTER EDGE OF THE FLANGE AND ADAPTED TO BE ENGAGED BY THE TAPERING SIDE OF A PROJECTION OF A SIMILARLY FORMED SEAL BLANK TO SECURE THE BLANKS TOGETHER IN NESTED RELATIONSHIP WITH SLIGHT MOVEMENT OF THE NESTED BLANKS IN FOUR DIRECTIONS, SAID BLANKS BEING DISENGAGED BY SLIDING ONE BLANK RELATIVE TO THE OTHER SO THAT ONE SLOPING END OF THE PROJECTION WILL SLIDE ON A SLOPING END WALL OF THE SLOT IN WHICH THE PROJECTION IS ENGAGED. 